Note 20 — Chapter VI · THE SPREAD OF ISLAM AMONG THE CHRISTIAN NATIONS IN EUROPE UNDER THE TURKS.
Reading edition
Scanty as these notices of conversion are, they appear to have been voluntary, and the Zoroastrians would seem to have enjoyed on the whole toleration for the exercise of their religion up to the close of the ʻAbbāsid period. With the Mongol invasion a darker period in their history begins, and the miseries which the Persian Muslims themselves suffered seems to have generated in them a spirit of fanatical intolerance which exposed the Zoroastrians at times to cruel sufferings.20